1. Field of the Invention
The present invention relates to reaction products of aminoalkylenecarboxylic acids, which products are suitable as paraffin dispersants, and their use and mineral oil middle distillate compositions which are based on a hydrocarbon mixture and contain these reaction products.
2. Discussion of the Background
Middle distillates, for example gas oils, diesel oils or fuel oils, which are obtained by distillation of mineral oils, have different paraffin contents, depending on the origin of the crude oil. At relatively low temperatures, solid paraffins separate out (cloud point, CP). On further cooling, the lamellar n-paraffin crystals form a house-of-cards structure and the middle distillate sets although the predominant part of the middle distillate is still liquid. The flow of the mineral oil middle distillates is considerably adversely affected by the precipitated n-paraffins between the cloud point and the pour point. The paraffins block filters and cause irregular fuel feed to the combustion units or completely stop this feed.
It has long been known that the crystal growth of the paraffins in the mineral oil middle distillates can be modified by suitable additives. Effective additives on the one hand prevent middle distillates from forming such house-of-cards structures and becoming solid at temperatures a few degrees Centigrade below the temperature at which the first paraffin crystals crystallize out and, on the other hand, result in the formation of fine, well crystallized, separate paraffin crystals which pass through filters in motor vehicles and heating systems or at least form filter cakes which are permeable to the liquid part of the middle distillates, thus ensuring trouble-free operation.
A disadvantage of this prior art is based on the fact that the precipitated paraffin crystals have a higher density than the liquid part and therefore tend to settle out on the bottom of the container to an increasing extent during storage. This results in the formation of a homogeneous phase having a low paraffin content in the upper part of the container and a two-phase paraffin-rich layer at the bottom. Since the middle distillate is generally taken off slightly above the bottom of the container both in vehicle tanks and in the storage and delivery tanks of mineral oil dealers, there is a danger that the high concentration of solid paraffins will lead to blockage of filters and metering means. This danger is all the greater the further the storage temperature is below the precipitation temperature of the paraffins (cloud point), since the amount of paraffin precipitated is a function of the temperature and increases with decreasing temperature.
The paraffin crystal modifiers, ie. is flow improvers, are polymers which change the crystal growth of the n-paraffins by cocrystallization (interaction). The flow properties of the middle distillate at relatively low temperatures are advantageously affected. The efficiency of the flow improvers is expressed indirectly by measurement of the cold filter plugging point (CFPP), according to DIN 51,428.
Conventional ethylene copolymers, especially copolymers of ethylene and unsaturated esters, are used as low-temperature flow improvers. DE 11 47 799 and DE 19 14 756 describe, for example, copolymers of ethylene with vinyl acetate, containing from 25 to 45% by weight of vinyl acetate or vinyl propionate and having a molecular weight of from 500 to 5,000.
Furthermore, GB 2 095 698 discloses that a combination of the stated copolymers with amides of long-chain amines and aromatic or cycloaliphatic carboxylic acids can be added to middle distillates.
However, these mixtures are still unsatisfactory with regard to the dispersing properties of the precipitated paraffins. It is therefore necessary for the additives introduced also to effect dispersing of the precipitated paraffins.
EP-A 398 101 discloses reaction products of aminoalkylenepolycarboxylic acids with long-chain secondary amines, which have been completely reacted with the amines to give the amide or ammonium salt, as paraffin dispersants.
The non-prior-published German Application P 4237662.9 relates to reaction products of amino-alkylenepolycarboxylic acids of long-chain secondary amines, in which free carboxyl groups or alkali metal or alkaline earth metal carboxylate groups are still present.
These paraffin dispersants are commercially available in general in the form of a concentrated solution in oil-soluble solvents, such as high-boiling petroleum ethers or mixtures of aromatics. However, in concentrated solution, these dispersants may have such a high pour point that they are more difficult to handle during transfer or metering.